Two photon resonance enhanced multiphoton ionization spectroscopy of gas phase O a Δ between 305350 nm (original) (raw)
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Resonance-enhanced multiphoton ionisation spectroscopy of the NH(ND) radical. Part 1?The d 1?+ state
Journal of the Chemical Society, Faraday Transactions, 1991
Rydberg excited states of the OCS molecule in the energy range 70500-86000 cm Ϫ1 have been investigated via the two and three photon resonance enhancements they provide in the mass resolved multiphoton ionization ͑MPI͒ spectrum of a jet-cooled sample of the parent molecule. Spectral interpretation has been assisted by companion measurements of the kinetic energies of the photoelectrons that accompany the various MPI resonances. The present study supports the earlier conclusions of Weinkauf and Boesl ͓J. Chem. Phys. 98, 4459 ͑1993͔͒ regarding five Rydberg origins in the 70500-73000 cm Ϫ1 energy range, attributable to, respectively, states of 3 ⌸, 1 ⌸, 3 ⌬, 1 ⌬ and 1 ⌺ ϩ symmetry arising from the 4p←3 orbital promotion. We also identify a further 21 Rydberg origins at higher energies. These partition into clumps with quantum defects ca. 3.5 and 4.5, which we associate with the orbital promotions np←3 (nϭ5,6), and others with near integer quantum defect which are interpretable in terms of excitation to s,d and ͑possibly͒ f Rydberg orbitals. We also identify MPI resonances attributable to CO(X 1 ⌺ ϩ) fragments and to S atoms in both their ground (3 P) and excited (1 D) electronic states. Analysis of the former resonances confirms that the CO(X) fragments resulting from one photon dissociation of OCS at excitation wavelengths ca. 230 nm are formed with a highly inverted, bimodal rotational state population distribution, whilst the latter are consistent with previous reports of the wavelength dependence for forming ground and excited state S atoms in the near uv photolysis of OCS.
Applied Physics B, 1983
Resonance-enhanced nmltiphoton ionization (REMPI) of the /~ and C' states of NH 3 in a pulsed supersonic molecular beam was observed at 30~340nm, using the multiphoton-ionization mass-spectrometer system described herein. The observed features are the result ofa 2 + 1 MPI process and correspond quite well with the reported 3 + 1 MPI of NH 3 in the literature from the: ground state of opposite parity.
Multiphoton ionization of methyl radicals in the gas phase
The Journal of Physical Chemistry, 1982
The technique of mass-selected multiphoton ionization (MPI) has been applied to the detection of gas-phase methyl radicals. Methyl radicals were produced by pyrolysis of various CH, sources in a resistively heated tantalum oven. The output of a Nd:YAG pumped dye laser was focused into the ionization region of a quadrupole mass spectrometer. The mass-selected multiphoton ionization spectrum was obtained by measuring the mass 15 ion signal as a function of dye laser wavelength. Methyl radicals were identified by observing CH, Rydberg-state resonances in the MPI spectrum. The three-photon Rydberg states are assigned along with the associated vibronic transitions. The results are discussed in terms of the vibronic structure of the electronically excited Rydberg states. These results indicate the general applicability of multiphoton ionization to the detection of nonfluorescing free radicals.
Multiphoton ionization spectroscopy of ClO and BrO
The Journal of Chemical Physics, 1985
We report the resonance enhanced multiphoton ionization spectra ofCIO and BrO free radicals between 415 and 475 nm. The observed electronic states were prepared by simultaneous absorption of three identical photons from a dye laser. Absorption of at least one additional photon induced ionization. CIO showed spectra originating from the D, E, and F states previously reported by N. Basco and R. D. Morse. The origin of the F 2 .I...-X 2IIi bands were reassigned to 1'00 = 70 183 cm-I and 1'00 = 69 868 cm-I. BrO showed three new vibrational progressions originating from transitions between the X 2 II3/2 state to Rydberg states with assignments of E 2.I (1'00 = 65 003 cm-I), F 2 .I (1'00 = 67 470 cm-I), and an apparently inverted state, designated G (1'00 = 70 504 cm-I), that possesses orbital angular momentum greater than zero. The G-state bands were separated by 139(± 3) cm-I which should approximate the magnitude of the spinorbit coupling constant of this excited state if it is of2IIi symmetry.
Chemical Physics, 2001
The absolute multi-photon ionization cross-section of the phenyl ring was determined by laser-ionization of toluene and xylene molecules in the gas phase. Excitation was achieved using nonresonant four-photon absorption of the frequency doubled light of a 10 ns pulsed Nd:YAG laser (532 nm). The resulting ions were stored in a Penning trap and detected by time-of-¯ight mass spectrometry. The values of the cross-sections are 1:43 Â 10 À42 cm 8 W À4 s À1 and 1:33 Â 10 À42 cm 8 W À4 s À1 for toluene and xylene, respectively. Ó
Multiphoton excitation and ionization of atoms and molecules
La Rivista del Nuovo Cimento, 1989
The two-photon excitation and three-photon ionization of atomic cesium is investigated over the 6550-6950-A wavelength region with a tunable-dye-laser source having a 0.06-0.0S-A. linewidth and a space-charge ionization detector sensitive to a few iona per second. An online data-acquisition computer provides significant signal-to-noise recovery. The resulting dispersion curve for photoionization is interpreted in terms of the two-photon transitions from the ground 628&y2 level to resonant n D and n 8 intermediate states, and represents, to the authors'knowledge, the first such two-photon absorption spectrum of Cs. Transitions from n =9 to 13 have been recorded for the 6 Qy2n Dg(2 3/2 series and from n =11 to 14 for the 62+g2n 2@F2 series.
Spectrochimica Acta Part B: Atomic Spectroscopy, 1997
The temporal behavior of the laser enhanced ionization signal of mercury was studied in a quartz cell under low buffer gas pressure. Using fast electronics and a short (34 ns) laser pulse, it was possible to distinguish, in one single time-resolved ionization waveform, the non-selective photoionization component of the signal from that which was due to collisional ionization from selected levels. Experimental results were shown to agree with those obtained by computer simulation, and optimal conditions for deconvolution of the two components were studied. © 1997 Elsevier Science B.V.
Gas-phase infrared multiple photon dissociation spectroscopy of mass-selected molecular ions
International Journal of Mass Spectrometry, 2006
In this review, we present an overview of our recent work on the infrared spectroscopy of mass-selected gas-phase molecular ions. The ions are stored and isolated in a quadrupole ion trap where they are investigated with infrared multiple photon dissociation spectroscopy using a free electron laser (FEL). The wide and continuous tunability of FELIX, the FEL for Infrared eXperiments at the FOM institute for Plasma Physics in The Netherlands, allows us to explore the interesting mid-infrared range between 500 and 2000 cm−1, sometimes referred to as the fingerprint region. The experiments have focused on polycyclic aromatic hydrocarbons because of their hypothesized occurrence in the interstellar medium, both in neutral and cationic forms. Furthermore, several related species of fundamental chemical interest have been investigated, such as molecular fragment ions and protonated species. The spectra are compared to theoretical spectra calculated at the density functional theory level. The effects of multiple photon excitation and dissociation dynamics on the appearance of the spectrum are extensively discussed. A mathematical model to account for the effects of anharmonicity is described. It explains for instance, qualitatively, how the observed spectral response can vary (slightly) with the fragment channel, which allows one to “direct” dissociation reactions in a non-coherent fashion by the choice of the infrared excitation wavelength.
Chemical Physics Letters, 1996
Progression of bands associated with the v 2 (bending) vibrational mode of the F.'l,(1 (4pa'~ ~ 3a l) Rydberg states of both NH 3 and ND 3 have been observed as two-photon resonances in the multiphoton ionisation spectrum of these two isotopomers at excitation wavelengths in the range 275-248 nm. Band contour analysis yields excited state spectroscopic parameters and some insight into the predissociation behaviour of these levels, all of which show many parallels with previous knowledge concerning the C'I.~ 1 Rydberg state of ammonia (arising from the corresponding 3pa'~ *-3a I orbital promotion).